The Copernican Period in the lunar geologic timescale runs from approximately 1.1 billion years ago to the present day. The base of the Copernican period is defined by impact craters that possess bright optically immature ray systems. The crater Copernicus is a prominent example of rayed crater, but it does not mark the base of the Copernican period. No mare basalts are known to have erupted within the Copernican period, and for this reason, the Moon's internal geologic activity is thought to have effectively ceased by this time.
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Famous quotes containing the word period:
“Stupid word, that. Period. In America it means “full stop” like in punctuation. That’s stupid as well. A period isn’t a full stop. It’s a new beginning. I don’t mean all that creativity, life-giving force, earth-mother stuff, I mean it’s a new beginning to the month, relief that you’re not pregnant, when you don’t have to have a child.”
—Michelene Wandor (b. 1940)